The IEEE Low Rate Wireless Personal Area Network (LR-WPAN) Medium Access Control (MAC) standard 802.15.4 specifies a superframe structure that has a Beacon, Contention Access Period (CAP), and Contention Free Period (CFP). During the CAP, transmissions take place utilizing a Carrier Sense Multiple Access (CSMA) technique. In CSMA, if the channel is idle (i.e., no other transmissions are occurring), transmission can take place; otherwise, the device waits (“backs off”) a random period of time and attempts to transmit again. Therefore, a device attempting to transmit is required to utilize a receiver to monitor the channel prior to transmission (i.e., to perform a “clear channel assessment,” or CCA). Unlike transmissions in the CAP, transmissions in the CFP are contention free. Particularly, each node is assigned its own unique epoch, slot, or portion of the CFP to transmit within. No other nodes will be transmitting during a particular node's CFP, so transmissions may take place without CSMA.
Quality of Service (QoS) can be achieved using the CFP. However, sometimes it is also desirable to achieve QoS in the CAP of a superframe. For example, some systems (like neuRFon) using 802.15.4 may only support a CAP in order to reduce the code size of the MAC and/or to operate in very low-duty cycle operations. However, QoS cannot be guaranteed because the CAP uses Carrier Sense Multiple Access (CSMA), and therefore the time when a user can access the communication channel is unpredictable. An outstanding question for such systems that have communication sessions with time requirements is how to implement QoS over MACs that make use of CAPs or Beacons and CAPs solely without CFPs. Therefore, a need exists for a method and apparatus for providing quality of service over a contention access period of a wireless personal area network.